Detailed information about the interface between actin and myosin is needed for a better understanding of various aspects of the actin-myosin interaction underlying the crossbridge cycle of muscle contraction. We also need information on the interaction between myosin heavy chains and light chains to understand the function of light chains and the topography of myosin S-1. In view of the importance attributed to the so-called hinge regions in the in vivo motion of myosin cross-bridges, information on the conformation of various portion of the rod is desirable. Thus the application will focus on the following specific aims: 1). Identification of the interface regions using a number of bifunctional crosslinkers under a variety of conditions. 2). Completion of the determination of the primary structure of myosin rod. 3). Exploration of the conformation of different portions of myosin rod by examining the ability of sulfhydryls to form disulfide bonds and the susceptibility of these regions to proteolytic enzymes under various conditions. 4). Localization of light chains in relation to heavy chains by crosslinkling experiments. 5). Crosslinking studies of LMM and identification of the interaction regions with a view to obtaining information relevant to filament formation. The knowledge of normal muscle will serve as a reference and may eventually prove useful in the diagnosis, treatment, and prevention of disease involving muscle tissue and the cardiovascular system.